We propose to develop a tank-based microwave thermal imaging system for monitoring temperature profiles in breast tissue during hyperthermia treatments. Based on encouraging Phase II clinical trials for breast cancer treatment, complete response rates were shown to improve significantly when hyperthermia was added to radiation treatment protocols. This work will draw on the feasibility study conducted during Phase I where we demonstrated the capability of quantitatively monitoring temperatures to within 1 degree Celcius and a spatial resolution of 1 cm. Efforts by the Dartmouth College microwave imaging research group to develop a clinical breast cancer detection system has also established the feasibility of in vivo microwave breast imaging using a water-coupled interface in the clinical environment. The key components of Phase II will include refining the prototype clinical patient interface and integrating it with a scanned focused ultrasound hyperthermia device. A primary objective of Phase II will be to develop a clinical prototype system where data can be collected for image reconstruction at several vertical positions in less than one minute with quantitative difference images being available as treatment feedback information within 2 minutes after collection of each data set. Initial overall performance assessments will be conducted using phantom and ex vivo experimental configurations. PROPOSED COMMERCIAL APPLICATION: Breast cancer treatment remains an important health care problem. This system will facilitate the use of adjuvant hyperthermia by providing a low-cost noninvasive monitoring technique. It addresses previous difficulties associated with noninvasive temperature detection by providing near real-time data acquisition and expedited image reconstruction along with fabrication of an effective patient interface. It will set the stage for future treatment/monitoring systems targeting other anatomical sites.